This invention relates to thermally-assisted magnetic recording (TAMR) where data is written while the magnetic recording layer is at an elevated temperature, and more particularly to a TAMR disk that has a multilayered thermal barrier located between the disk substrate and the magnetic recording layer.
Magnetic recording disk drives store digital information by using a very small thin film inductive write head. The write head is patterned on the trailing surface of a slider that also has an air-bearing surface (ABS) to allow the slider to ride on a thin film of air above the surface of the rotating disk. The write head is an inductive head with a thin film electrical coil located between the poles of a magnetic yoke. When write current is applied to the coil, the pole tips provide a localized magnetic field across a gap that magnetizes the recording layer on the disk into one of two distinct magnetic states (binary data bits).
The magnetic material for use as the recording layer on the disk is chosen to have sufficient coercivity such that the magnetized data bits are written precisely and retain their magnetization state until written over by new data bits. The data bits are written in a sequence of magnetization states to store binary information in the drive and the recorded information is read back with a use of a read head that senses the stray magnetic fields generated from the recorded data bits. Magnetoresistive (MR) read heads include those based on anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), such as the spin-valve type of GMR head, and the more recently described magnetic tunnel junction (MTJ) effect. Both the write and read heads are kept in close proximity to the disk surface by the slider""s ABS, which is designed so that the slider xe2x80x9cfliesxe2x80x9d over the disk surface as the disk rotates beneath the slider.
Disk drive areal data density (the number of bits that can be recorded on a unit surface area of the disk) is now approaching the point where the data bits are so small they can be demagnetized simply from thermal agitation within the magnetized bit (the so-called xe2x80x9csuperparamagneticxe2x80x9d effect). The conventional approach to circumventing this problem is to increase the magneto-crystalline anisotropy and coercivity of the magnetic material in the recording layer on the disk to improve the thermal stability. However, this requires that the write head be made with a material with high saturation moment to increase the write field of the head so the head can write on the high coercivity media.
Since it is known that the coercivity of the magnetic (i.e., the magnetic recording layer on the disk) is temperature dependent, one proposed solution is thermally-assisted magnetic recording (TAMR), wherein the magnetic material in the media is heated locally to near or above its Curie temperature during writing so that the coercivity is low enough for writing to occur, but high enough for thermal stability of the recorded bits at ambient temperature. Several approaches to TAMR have been proposed, including use of a laser beam or ultraviolet lamp to do the localized heating, as described in xe2x80x9cData Recording at Ultra High Densityxe2x80x9d, IBM Technical Disclosure Bulletin, Vol. 39, No. 7, July 1996, p. 237; xe2x80x9cThermally-Assisted Magnetic Recordingxe2x80x9d, IBM Technical Disclosure Bulletin, Vol. 40, No. 10, October 1997, p. 65; and IBM""s U.S. Pat. No. 5,583,727. A read/write head for use in a TAMR system is described in U.S. Pat. No. 5,986,978, wherein a special optical channel is fabricated adjacent to the pole or within the gap of a write head for directing laser light or heat down the channel. IBM""s pending application Ser. No. 09/608,848 filed Jun. 29, 2000 describes a TAMR disk drive wherein the thin film inductive write head includes an electrically resistive heater located in the write gap between the pole tips of the write head for locally heating the magnetic recording layer.
In TAMR the magnetic recording media must be able to retain the heat from the heat source, whether a laser or resistive heater, so that the magnetic material in the locally heated spot can reach the required temperature and stay at that temperature for the required time. Thus the use of a low thermal conductivity material as a thermal barrier beneath the magnetic recording layer not only avoids rapid heat conduction away from the locally heated spot but also reduces the amount of power required at the heat source.
Multilayered thermal barriers are known as coatings for various components, such as turbine blades, as described in U.S. Pat. Nos. 5,687,699 and 5,998,003. These barriers typically comprise large numbers of bilayers or alternating layers of dissimilar dielectrics, such as alumina and zirconia, with each dielectric/dielectric interface acting as a phonon scattering zone. Multilayers of alternating dissimilar dielectrics are also known for regulating the reflection from a magneto-optic (M-O) recording layer, as described for up to five ZnS/MgF2 bilayers in U.S. Pat. No. 4,649,451. D. Josell et al., in xe2x80x9cThermal Diffusion Through Multilayer Coatings: Theory and Experimentxe2x80x9d, International Journal of Thermophysics, Vol. 19, No. 2, 1998, pp. 525-535, studied a thermal barrier of multiple bilayers of molybdenum/alumina, where each layer was greater than 1000 Angstrom, and concluded there was no difference in thermal conductivity from comparable metal/metal multilayers.
What is needed is TAMR disk with an effective low-conductivity thermal barrier beneath the magnetic recording layer.
The invention is a TAMR disk that has a low thermal conductivity multilayered thermal barrier between the substrate and the magnetic recording layer to avoid rapid heat conduction away from the locally heated spot and to reduce the amount of power needed to raise the temperature of the recording media above a required value. The barrier comprises a plurality of alternating layers or bilayers of a metal having a high electrical resistivity, preferably greater than approximately 100 microOhm-cm, and a dielectric selected from the group consisting of oxides, nitrides and oxynitrides of one or more of Al and Si. The large number of metal/dielectric interfaces, each with high thermal resistance, reduces the out-of-plane thermal conductivity of the barrier, and the use of high electrical resistivity metal layers minimizes in-plane heat spreading.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.